This invention relates to an air/hydraulic system for raising and lowering a load, such as for use on with a trailer or the like.
Various systems are known and used for lifting and lowering of a load such as a trailer. In most such systems, it is generally necessary for pressurized air to be supplied to the system whenever it is desired to raise or lower the legs. Further, such systems generally require a pair of oil reservoirs, one of which supplies oil to a booster pump for extending the legs, and the other of which provides oil under pressure for retracting the legs by means of a manual retraction pump or the like.
The present invention is designed to provide a simplified system for raising and lowering legs for use on a trailer or the like. In accordance with the invention, a pressurized fluid operated lifting and lowering system includes one or more fluid operated extendible and retractable legs, with each leg including biasing means urging the leg to retract. Lock valve means is associated with each leg and is movable between an open position and a closed position. The lock valve means in its open position allows fluid flow to or from the leg, and in its closed position prevents fluid flow to or from the leg. The lock valve means preferably includes a movable internal member which selectively allows fluid flow therethrough. The lock valve means is normally urged to its closed position.
Selectively actuable extension means is provided for moving the lock valve means to its open position and selectively supplying pressurized fluid to the leg to overcome the biasing means and to cause the leg to extend. To extend the legs under load, a booster pump is manually actuated by means of a booster valve which selectively supplies pressurized air to the booster pump. The booster pump draws fluid from the reservoir, and pumps intensified fluid pressure to the legs to extend the legs. Operation of the booster pump provides pressurized fluid to the lock valve, which opens the lock valve and passes into the leg for extending the leg. When pressurized fluid is not supplied to the lock valve, the lock valve returns to its closed position to prevent fluid flow therethrough.
Selectively actuable retraction means is provided for moving the lock valve means to its open position. The retraction means preferably includes means for simultaneously cutting off the supply of pressurized air to the system when the lock valve means is moved to its open position. When this occurs, fluid is allowed to be expelled from the leg due to retraction of the leg by the action of the biasing means. In a preferred embodiment, the retraction means is a pressurized fluid actuated system.
A master valve is provided for moving the lock valve to its open position when pressurized fluid is not supplied thereto, for allowing fluid to be expelled to retract the legs. The master valve is preferably interconnected with an air valve so that actuation of the master valve controls the supply of pressurized air to the system. The master valve is movable between an extend position and a retract position, with a neutral position midway between the extend and retract positions. The master valve is preferably interconnected with the fluid reservoir mentioned above, and in its retract position supplies fluid pressure to an external actuator which moves the lock valve to its open position for allowing fluid to flow therethrough to retract the legs. The master valve includes a piston disposed within a passage, with the passage being interconnected with the external lock valve actuating means. A first opening provides communication between the passage and the reservoir, and a second opening provides communication between the passage and the lock valve. A third opening provides communication between the legs and the reservoir. When in its retract position, the master valve piston covers the first opening to cut off the supply of fluid pressure thereto, while maintaining fluid pressure in the line communicating the passage with the external actuating means. In this position, the third opening is exposed so as to allow fluid flow from the leg through the lock valve and the third opening, and back into the reservoir. As noted, the supply of pressurized air to the reservoir is cut off and vented so as to allow flow of fluid to the reservoir.